Commercial catalytic processes for the production of polyolefins, such as polyethylene and polypropylene, have traditionally relied on the use of heterogeneous, Ziegler-Natta catalyst systems. Typical catalyst systems for polyethylene are exemplified by Chromium compositions supported on silica and Titanium compositions on MgCl2. Although the catalyst systems are quite active and can produce high molecular weight polymers, they tend to produce a broad molecular weight distribution of a particular polyolefin and are poor at incorporating alpha-olefins such as 1-hexene and 1-octene. When making copolymers of ethylene, these catalysts typically produce resins of moderately broad to very broad molecular weight distribution, as characterized by MWD values greater than 6. Lack of a narrow molecular weight distribution in such catalyst systems is believed due to the presense of more than one type of catalytic site.
More recently, olefin polymerization catalyst systems containing well defined reactive sites have been developed. So-called “Single-site catalysts” allow for the production of polymers with varied molecular weights, narrow molecular weight distributions and the ability to incorporate large amounts of comonomers. Metallocene catalysts based on Group 3–6 metals of the Periodic Table (IUPAC nomenclature) containing cyclopentadienyl groups and transition metal catalysts based on Group 3–10 metals of the Periodic Table (IUPAC nomenclature) containing bi- or tridentate ligands are examples of these active single-site catalysts. Such catalysts have been disclosed in U.S. Pat. Nos. 5,064,802; 5,198,401; 5,342,800; 5,866,663 and publications WO 96/23010; WO 98/30612.
The mechanism of olefin polymerization using the above mentioned catalysts has been the subject of much study and is believed to involve generation of an unsaturated, electron deficient metal species, which coordinates olefins to form intermediate alkyl olefin complexes, then subsequently undergoes rapid alkyl migration to afford a growing polymer chain. Olefin coordination followed by migration (insertion) continues until a termination step occurs or the reaction is stopped.
Several methods are currently employed to generate and stabilize the unsaturated electron deficient metal catalysts of such systems. The activation of transition metal complexes to afford stabilized, unsaturated transition metal catalysts for the polymerization of olefins is a key part of this mechanism. Several methods are currently employed to generate and stabilize the unsaturated, electron deficient metal catalysts of such systems and include halide abstraction, protonation followed by reductive elimination, or oxidation. A key element of the activation process is the stabilization of the resulting activated complex using non-coordinating anions. For example, halide containing transition metal complexes can be activated using methylalumoxane (MAO). MAO serves as both a methylating agent and as a non-coordinating anion. Other activating components of utility containing boron include silver tetraphenyl borate, triphenylcarbenium tetrakis(pentafluorophenyl) borate, tri(pentafluorophenyl) boron, N,N-dimethylanilinium tetra(pentafluorophenyl) borate and sodium tetrakis[3,5-bis(trifluoromethyl)-phenyl] borate. Catalyst systems using such activators have been disclosed in U.S. Pat. Nos. 4,808,561; 4,897,455; 4,921,825; 5,191,052; 5,198,401; 5,387,568; 5,455,214; 5,461,017; 5,362,824; 5,498,582; 5,561,092; 5,861,352 and publications WO 91/09882; EP0206794B1; EP0507876B1; WO 95/15815; WO 95/23816; EP0563917B1; EP0633272A1; EP0633272B1; EP0675907B1; JP96-113779; EP0677907B1; WO 98/55518; WO 00/04059.
The greatest utility of single-site catalyst systems to the polyolefin industry is realized when they are used in gas phase and slurry phase reactors. Inorganic oxides such as silica, alumina and magnesia currently have the greatest utility as a support material in the formulation of supported Ziegler-Natta polyolefin catalyst systems. The inorganic supports have also been used with varying degrees of success in supporting metallocene and other types of single-site metal catalysts. A significant limitation of such supports, however, is the presence of surface hydroxyl groups, which render the metallocene catalysts inactive. To overcome this effect large quantities of MAO are used with varying degrees of success coupled with high costs associated using MAO as a support material. Polymeric supports, such as cross-linked polystyrene (PS) have been investigated as supports, since they contain no catalyst deactivating or “poisoning” groups. Methods to chemically anchor metallocene and other single-site metal catalysts to supports have also been developed. The most common methods involve tethering the single-site metal catlyst through a substituent on the cyclopentadlenyl ring, through the boron atom of non-coordinating borate activators, through a substituent on the bridge of ansa-metallocene catalysts or through the heteroatom in monocyclopentadienyl complexes.
Given the problems associated with broad molecular weight distributions of polyolefins produced using Ziegler-Natta catalysts, it is desirable to develop a composition incorporating such catalysts that provides polyolefins having relatively narrow molecular weight distributions, comparable to production of the same polyolefins obtained using more expensive and less utilized single-site catalysts. A composition for the production of a range of polyolefins comprising a material that reacts with a variety of olefin polymerization catalysts forming and stabilizes or activates the catalysts, in addition to merely supporting the catalyst, is desirable. There are no reports of a single material that can react with many of the catalyst systems, generally known in the art and used in the production of polyolefins. An olefin-based material has been discovered that reacts with a variety of olefin polymerization catalysts, forming a composition for the production of a range of polyolefins, that stabilizes or activates the catalysts in addition to merely supporting the catalyst. The olefin-based material has utility with commercial developed polyolefin catalyts, such as single-site catalysts and Ziegler-Natta type catalysts. A general process for the production of polyolefins using a matrix that comprises a broad range of polyolefin catalyst systems, that provides uniform dispersal of the catalyst, that stabilizes and activates the catalyst in the process would, therefore, be of great utility; global economic advantage and strategic value to the commercial manufacture of polyolefins.